Effects of internal waves on low frequency, long range, acoustic propagation in the deep ocean
Citable URI
https://hdl.handle.net/1912/2123Location
North Pacific OceanDOI
10.1575/1912/2123Keyword
Acoustic models; Underwater acoustics; Roger Revelle (Ship) Cruise LOAPEX; Melville (Ship) Cruise LOAPEXAbstract
This thesis covers a comprehensive analysis of long-range, deep-ocean, low-frequency, sound
propagation experimental results obtained from the North Pacific Ocean. The statistics of
acoustic fields after propagation through internal-wave-induced sound-speed fluctuations
are explored experimentally and theoretically.
The thesis starts with the investigation of the North Pacific Acoustic Laboratory 98-99
data by exploring the space-time scales of ocean sound speed variability and the contributions from different frequency bands. The validity of the Garret & Munk internal-wave
model is checked in the upper ocean of the eastern North Pacific. All these results impose hard bounds on the strength and characteristic scales of sound speed fluctuations one
might expect in this region of the North Pacific for both internal-wave band fluctuations
and mesoscale band fluctuations.
The thesis then presents a detailed analysis of the low frequency, broadband sound
arrivals obtained in the North Pacific Ocean. The observed acoustic variability is compared with acoustic predictions based on the weak fluctuation theory of Rytov, and direct
parabolic equation Monte Carlo simulations. The comparisons show that a resonance condition exists between the local acoustic ray and the internal wave field such that only the
internal-waves whose crests are parallel to the local ray path will contribute to acoustic
scattering: This effect leads to an important filtering of the acoustic spectra relative to
the internal-wave spectra. We believe that this is the first observational evidence for the
acoustic ray and internal wave resonance.
Finally, the thesis examined the evolution with distance, of the acoustic arrival pattern
of the off-axis sound source transmissions in the Long-range Ocean Acoustic Propagation
EXperiment. The observations of mean intensity time-fronts are compared to the deterministic ray, parabolic equation (with/without internal waves) and (one-way coupled) normal
mode calculations. It is found the diffraction effect is dominant in the shorter-range transmission. In the longer range, the (internal wave) scattering effect smears the energy in both
the spatial and temporal scales and thus has a dominant role in the finale region.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2007
Suggested Citation
Thesis: Xu, Jinshan, "Effects of internal waves on low frequency, long range, acoustic propagation in the deep ocean", 2007-09, DOI:10.1575/1912/2123, https://hdl.handle.net/1912/2123Related items
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